This invention relates to the modification of a natural zeolite known as clinoptilolite, to the use of the modified clinoptilolite in the preparation and transformation of hydrocarbons, and to the regeneration of the modified clinoptilolite after use.
Synthetic zeolite catalysts such as Zeolite Y have been used for many years in processes for hydrocarbon cracking. Further, in 1973 it was discovered that methanol can be converted to gasoline over a synthetic zeolite catalyst known as ZSM 5. However, ZSM 5 is not the optimum catalyst for the chemical industry because it results in the formation largely of gasoline. The chemical industry would prefer a process, and thus a catalyst for the process, which results in the formation of ethene, propene and butene as these products are more flexible for further use. Further, ZSM 5 is expensive.
Synthetic zeolite catalysts are also of interest for the conversion of natural gases to more useful products. For example, when the gas obtained from a natural gas field is essentially methane, the gas may be steam reformed to form carbon monoxide and hydrogen. Thereafter there are two possible synthesis routes. The carbon monoxide and hydrogen can be subjected to a Fischer Tropsch process which will produce a range of products or the gas can be converted to methanol and then to gasoline utilising a synthetic zeolite catalyst.
In an article in Applied Catalysis, 16 (1985) 249-253 by Sakoh, Nitta and Aomura, it is disclosed that a natural (i.e. naturally occurring) clinoptilolite from Futatsui, Japan, after modification, can be used in the conversion of methanol to light olefins. The modification of the natural clinoptilolite was carried out following two different procedures. The first procedure involved treating the natural clinoptilolite with 1M HCl at 80.degree. C. for 24 hours after which the sample was filtered off, washed with distilled water and dried in air. The second procedure involved impregnating the clinoptilolite with 0.05M and 0.5M H.sub.2 SO.sub.4, whereafter the samples were filtered off, dried in air and then calcined at 400.degree. C. for 3 hours in air. Thereafter, the catalysts were placed in a fixed bed continuous flow reactor under atmospheric pressure, and methanol vapor was carried through the reactor using helium as a carrier gas. Methanol was converted to hydrocarbons and water at the reaction temperature of 250.degree.-400.degree. C. over all the modified clinoptilolite catalysts. The hydrocarbons produced contained essentially aliphatic hydrocarbons. Further, this article discloses the regeneration of these catalysts by recalcination in air.